It is well known in the field of irrigation generally and rotating sprinklers particularly for a sprinkler device to emit a non-rotating stream from a fixed nozzle onto a rotating plate with substantially radial grooves that also establish a moment arm, causing the plate (often referred to as a "rotor plate") to rotate about the nozzle axis. The plate also reorients the stream from vertical to substantially horizontal, distributing the water in a circular pattern. The grooves of the rotor plate may be configured to produce different wetting patterns depending on specific site applications. In some cases, the rotation of the rotor plate is slowed by a brake or "motor" in order to maximize the throw radius of the stream. In other cases, the rotor may be of the free spinning type. Examples of such sprinkler constructions may be found in commonly owned U.S. Pat. Nos. Re. 33,823; 4,796,811; 5,297,737; 5,372,307; 5,439,174; and 5,588,595.
To get maximum distance of throw in a sprinkler described generally above, it is desirable that the emitting stream be as concentrated as possible. It has been found that to obtain such a concentrated stream, it is advantageous to configure the rotor plate to have a single closed water passage that resembles a curved tube which is slightly larger in cross sectional diameter than the stream that is exiting the nozzle. The water passage needs to be substantially constant in cross sectional diameter throughout its length except for a slight flare at the entrance to help capture the stream, and a slight taper to a slightly smaller diameter at the exit. Because the size of the tubular water passage has to be so close in size to the nozzle stream, and in order to conserve space, the entry flare cannot be very large, and sometimes a small amount of the nozzle stream does not enter the water passage, but rather sprays out between the nozzle exit and the water passage entrance. This is generally due to manufacturing tolerances, i.e., the rotor plate entrance is not always perfectly aligned over the nozzle exit.
In the past, and for somewhat closed sprinkler body architecture, this leakage spray impinges on the inside diameter of the sprinkler body and then drips down the riser pipe that supports the sprinkler. For sprinklers having a more open architecture, the leakage spray carries radially a few feet before dropping to the ground. In either case, the net result is an undesirable excess of water in the first few feet around the base of the sprinkler.